Fracture toughness and high-cycle fatigue behaviour of Al–Mg and Al–Mg–Sc–Zr alloys

Abstract

Tensile, fracture toughness and high-cycle fatigue tests were carried out on Al–Mg and Al–Mg–Sc–Zr alloys. Fracture morphology and the microstructure of the alloys were observed by SEM and TEM, etc. Al–Mg–Sc–Zr alloy with fibrous fine grain structure showed higher tensile strength and fracture toughness than Al–Mg alloy, which had a larger grain size and obvious recrystallisation. In high-cycle fatigue tests, Al–Mg–Sc–Zr alloy presented a higher fatigue limit owing to its finer grains and nanosized precipitates, which increased the difficulty of fatigue crack initiation. Al–Mg alloy presented a lower fatigue limit because crack initiation caused by slip is more likely to occur. However, its rougher fracture surfaces may be beneficial to hindering the propagation of macrocracks.